Why are emails going to Gmail spam despite good sender score and setup?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 Jul 2025
Updated 19 Aug 2025
10 min read
It can be incredibly frustrating when your emails land in the spam folder, especially when you've done everything right on the technical side. You've set up SPF, DKIM, and DMARC, your sender score looks good, and even an email testing tool gives your templates a near-perfect score. Yet, emails to Gmail accounts consistently end up in spam, with Gmail even suggesting that many emails from your subdomain were recently marked as spam. What gives?
This scenario is more common than you might think. While technical authentication (SPF, DKIM, DMARC) and a general sender score are crucial, Google's filtering system, like many other mailbox providers, considers a multitude of factors beyond the basics. It's a complex algorithm that looks at your entire sending behavior and recipient engagement. Let's delve into the less obvious reasons why your emails might be hitting the spam folder and how to fix them.
The silent reputation problem
One of the most frequent culprits, even with a seemingly good setup, is domain and IP reputation at the specific receiving mail server. While a public sender score might look healthy, a new sending domain or a new association between your domain and an IP (even a shared one) needs to build trust with Google's algorithms. Google looks at the combination of your IP and domain, not just each individually. So, if your subdomain is new to sending, it lacks a sending history, and that can trigger spam filters regardless of a high general sender score.
Even if you're using a shared IP from an ESP like Mailgun, the problem isn't necessarily with the IP's overall reputation. It's often about the specific domain's reputation in conjunction with that IP, especially for the recipient. Google Postmaster Tools can provide more specific insights into how Google views your domain and IP, but it requires a certain volume of mail to populate data. If you've only sent a few dozen test emails, it won't have enough information.
This initial phase, where Google is still getting to know your sending patterns, is crucial. If early emails receive negative signals (even if it's just a few test accounts mistakenly marking them as spam, or if they lack engagement), it can quickly harm your nascent reputation. The system errs on the side of caution with new senders, often initially placing emails in spam until trust is established. This explains why your emails might be flagged as spam despite a low overall spam rate on other tools.
The importance of email warming
The misconception
Relying solely on general sender scores and the assumption that shared IPs negate the need for warming up a new domain.
Initial outcomes
Emails landing in the spam folder, particularly at Gmail, due to a lack of sending history.
The reality
Domain reputation and the specific domain-IP pair must be built up with each mailbox provider, especially with sensitive ones like Google.
The solution
Implement a proper warm-up strategy, starting with small volumes of highly engaged recipients.
Email warming is the process of gradually increasing your email sending volume over time. This helps mailbox providers, like Gmail, recognize your sending patterns as legitimate and build a positive reputation for your domain and IP address. Even if your ESP (like Mailgun) tells you that a shared IP doesn't require warming, your specific *sending domain* still needs to establish its own reputation, especially when starting fresh. Google's filters are highly sophisticated and differentiate between a well-established sender and a new one, even if both are on the same shared IP.
To warm up effectively, start by sending small volumes to highly engaged recipients who are likely to open, click, and reply. Gradually increase the volume and the diversity of your audience. This consistent positive engagement tells Gmail that your emails are valued. Neglecting this step can lead to your emails being flagged as spam, as Google's system might interpret a sudden surge of mail from a new domain as suspicious behavior.
Even with perfect technical setup and a decent sender score, if you're sending to Gmail users who rarely open your mail, mark it as spam, or delete it unread, your deliverability will suffer. Gmail'sspam filters are heavily influenced by user engagement metrics. A high spam complaint rate, even from a few test emails, can be devastating to a new domain's reputation. This is why Google Postmaster Tools showing "many emails marked as spam" is a critical red flag, regardless of your overall sender score.
Similarly, the content of your emails plays a significant role. Even if Mail-Tester gives you a high score, real-world spam filters can be more discerning. Excessive use of promotional language, certain spam trigger words, unusual formatting, broken links, or misleading subject lines can all contribute to your emails being flagged as spam. Gmail is particularly sensitive to user feedback, and if recipients consistently mark your content as spam, it will negatively impact your sender reputation, regardless of your authentication setup.
Content, engagement, and list hygiene
Focus on high engagement
Target early emails: Send your initial warming emails to people who are highly likely to open and interact with them.
Monitor engagement: Track open rates, click-through rates, and reply rates. Positive engagement builds trust.
Clean your lists: Regularly remove inactive or invalid email addresses to avoid spam traps.
Even with SPF, DKIM, and DMARC configured, subtle issues can still lead to deliverability problems. For example, if your DMARC policy is set to p=none, it means you're only monitoring your email traffic, not actively instructing receiving servers to quarantine or reject unauthenticated mail. While a good starting point, Gmail and Yahoo's new 2024 requirements strongly encourage a p=quarantine or p=reject policy for bulk senders.
Alignment failures, even when SPF or DKIM technically pass, can also lead to issues. DMARC requires that the domain in your From: header (the one your recipients see) matches the domain that authenticated via SPF or DKIM. If there's a mismatch, even a technically valid SPF or DKIM record might not be enough to satisfy Gmail's stringent checks. You might pass basic authentication, but still fail at the alignment level, which Gmail considers for deliverability.
Finally, while you might check public blocklists (or blacklists) and find your IP and domain clean, many ISPs, including Google, maintain their own internal, private blocklists. If your domain or IP triggers their internal spam detection mechanisms due to unusual sending patterns, low engagement, or high complaint rates, you won't necessarily see it on external blocklist checkers. This is why Google Postmaster Tools, once you have sufficient volume, is often the most accurate reflection of your sending status with Google.
Advanced authentication and hidden issues
SPF record example for MailgunDNS
v=spf1 include:_spf.mailgun.org ~all
The phrase "many emails from our subdomain have been recently marked as spam" directly from Gmail is the most important clue. This indicates a reputation problem with your specific sending domain at Google. It's not necessarily a technical misconfiguration of SPF, DKIM, or DMARC, but rather how Gmail perceives your sending behavior for that particular subdomain. This perception is built on user interactions (or lack thereof) and internal signals, which a new subdomain doesn't have positive history for yet. Sender reputation is crucial.
Even if your Mail-Tester score is high, it evaluates technical configuration and content against a general set of rules. It doesn't simulate real-world recipient behavior or Google's internal, proprietary algorithms, which are heavily influenced by engagement. A handful of early spam complaints, even unintentional ones from test accounts, can disproportionately impact the reputation of a new sending domain. This is why you must understand why your emails are failing.
This challenge highlights the need for a comprehensive approach to email deliverability, beyond just checking boxes for technical setup and basic scores. It's about nurturing your sender reputation from day one, particularly with key mailbox providers. You can read more about how to check and improve email sender reputation to dive deeper.
Bridging the gap: good setup vs. Gmail's reality
Factor
Impact on deliverability
Monitoring tool
Domain reputation
How trusted your sending domain is based on history and user feedback.
The key takeaway is that deliverability is a dynamic process. While initial technical setup is fundamental, it's just the starting point. Mailbox providers, especially Gmail, continuously assess your sending reputation based on ongoing interactions and behavior. For a new sending domain, even with good authentication and a solid sender score, establishing trust takes time and consistent positive signals. This includes warming up your sending volume, ensuring high engagement, maintaining pristine list hygiene, and carefully crafting your content to avoid spam triggers. By focusing on these often-overlooked aspects, you can significantly improve your chances of landing in the inbox.
Views from the trenches
Best practices
Always implement a gradual email warm-up for new domains and new IP combinations, even if using shared IPs from an ESP.
Prioritize positive user engagement metrics like opens and clicks, as these significantly influence inbox placement, especially with Gmail.
Continuously monitor your domain and IP reputation using Google Postmaster Tools for specific insights into deliverability at Gmail.
Common pitfalls
Assuming that a good general sender score or shared IP automatically guarantees inbox placement for a new sending domain.
Neglecting to warm up a new sending domain, leading to immediate reputation issues with mailbox providers like Gmail.
Failing to analyze email content for potential spam triggers, even after receiving a high score from basic mail testing tools.
Expert tips
For new sending domains, closely monitor early engagement and spam complaint rates, as these set the tone for your long-term reputation.
Understand that content can override perfect technical setup; focus on providing value and avoiding promotional overkill, especially for transactional emails.
Remember that mailbox providers maintain internal, private blacklists (blocklists) not visible through public checks, making continuous reputation management essential.
Marketer view
Marketer from Email Geeks says that even with a shared IP, warming up the domain and IP relationship is necessary.
2019-12-06 - Email Geeks
Marketer view
Marketer from Email Geeks recommends specifically warming up sending to Gmail accounts.
2019-12-06 - Email Geeks
Overcoming deliverability hurdles
When emails from a domain with a seemingly good sender score and proper technical setup still land in Gmail's spam folder, it's often a signal that mailbox providers are looking beyond basic authentication. Gmail's sophisticated filters prioritize user engagement and the specific reputation of your domain-IP pairing. This means even with a clean technical slate, if your sending domain is new or if initial interactions are negative, you'll face an uphill battle. The solution lies in a multi-faceted approach, focusing on gradual warming, content quality, list hygiene, and constant monitoring of provider-specific reputation metrics.
It's essential to remember that email deliverability is a marathon, not a sprint. Building and maintaining a stellar sending reputation requires continuous effort, adaptation to evolving ISP rules (like Google and Yahoo's 2024 requirements), and a deep understanding of what individual mailbox providers deem trustworthy. By addressing these nuances, you can navigate the complexities of email deliverability and ensure your legitimate messages reach the intended inboxes.
Gmail accounts consistently end up in spam, with Gmail even suggesting that many emails from your subdomain were recently marked as spam. What gives?
Google's algorithms. Google looks at the combination of your IP and domain, not just each individually. So, if your subdomain is new to sending, it lacks a sending history, and that can trigger spam filters regardless of a high general sender score.
Gmail, due to a lack of sending history.
Yahoo's new 2024 requirements strongly encourage a p=quarantine or p=reject policy for bulk senders.
